This invention relates to liquid applicators including paint markers and ball-point pens particularly to those obtained by coupling a lead side shaft with a bottom side shaft by means of ultrasonic adhesion.
Conventionally, there has been sometimes used an ultrasonic adhesion method in fabricating a liquid applicator as a means for coupling a lead side shaft with a bottom side shaft, for example, for coupling a lead portion with a casing or coupling the casing with a bottom cap.
FIG. 11A shows an example of structure in which casing 80 is coupled with a lead portion 82 in a liquid applicator as described above. In this figure, the hollow cylindrical casing 80 has an outer stepped portion 84 and an inner stepped portion 86 formed radially side by side. A lead end face 85 of the outer stepped portion 84 is located more toward a lead end of the liquid applicator (toward the left side in FIG. 11A) than a lead end face 87 of the inner stepped portion 86. On the other hand, the hollow cylindrical lead portion 82 has first, second, and third stepped portions 88. 90. 92 in this order from a radially outermost one. A bottom end face 95 of the second stepped portion 90 is located more toward a bottom end of the liquid applicator (toward the right side in FIG. 11A) than a bottom end face 94 of the first stepped portion 88. A bottom end face 96 of the third stepped portion 92 is located more toward the bottom end of the liquid applicator than the bottom end face 95 of the second stepped portion 90.
In a state where the bottom end face 94 of the first stepped portion 88 is substantially in contact with the lead end face 85 of the outer stepped portion 84 or the faces 85, 94 are slightly spaced apart, the lead end face 87 of the inner stepped portion 86 is coupled with the bottom end face 95 of the second stepped portion 90 by means of ultrasonic adhesion. The first stepped portion 88 and the outer stepped portion 84 are formed so as to prevent resin or the like melted by the ultrasonic waves from pouring out.
In the case where an excessive bending load F, for example, as shown in FIG. 11B acts on the liquid applicator main body in the above structure, the casing 80 is lifted from the lead portion 82 about an inner corner 98 of the outer stepped portion 84 which serves as a fulcrum of a lever. Thus, the lead end face 87 of the outer stepped portion 86 and the bottom end face 95 of the second stepped portion 90 coupled by the ultrasonic adhesion are liable to come apart. This leads to a loss of airtightness in the liquid applicator (particularly those of the core type or the free ink type). Accordingly, it has become critical to prevent the loss of airtightness in the interior of the liquid applicator.
In view of the problems residing in the prior art, it is an object of the present invention to provide a liquid applicator having lead and bottom side shafts coupled with each other by means of ultrasonic adhesion which is capable of preventing adhered faces from being separated at an adhered portion, and a fabricating method thereof.
Accordingly, the invention is directed to a liquid applicator consisting essentially of a hollow lead side shaft and a hollow bottom side shaft coupled with the lead side shaft in an axial direction of the liquid applicator. The lead side shaft includes a plurality of lead stepped portions arranged side by side radially of the liquid applicator such that bottom end faces thereof are located at positions different from one another in the axial direction. The bottom side shaft includes a plurality of bottom stepped portions arranged side by side radially of the liquid applicator such that lead end faces thereof are located at positions different from one another in the axial direction and are opposed to the bottom end faces of the corresponding lead stepped portions. At least two of the bottom end faces of the lead stepped portions are adhered with the corresponding lead end faces of the bottom stepped portions by means of ultrasonic adhesion.
With the liquid applicator thus constructed the ultrasonic adhesion is carried out between the plurality of lead and bottom stepped portions which are located at radially and axially different portions on the lead and bottom side shafts. Accordingly, the case where a bending load F as shown in FIG. 11B acts on the liquid applicator, a fulcrum does not concentrate on a single point. Rather, fulcrums exist at a plurality of points. Thus, the burden at the adhered portion accompanied by the action of the bending load is reduced in terms of the strength, preventing the adhered faces from coming apart. If an exceedingly large bending load should act on the liquid applicator to cause the adhered faces to come apart at one adhered portion, the energy of this bending load is absorbed by the above separation and the adhered faces are prevented from coming apart at the other adhered portions. Therefore, the remaining adhered portions are allowed to maintain the coupling of the lead and bottom side shafts and airtightness in the liquid applicator. Of course, the axial adhesion strength can be enhanced by increasing the number of adhered portions.
A method of fabricating the above liquid applicator is preferably such that a projected portion is formed on at least either one of the bottom end face of the lead stepped portion and the lead end face of the bottom stepped portion to be adhered with each other so as to project toward the other end face, and ultrasonic waves are supplied in a state where the projected portion is in contact with the other end face.
According to this fabricating method, the projected portion formed on at least either one of the end faces to be adhered with each other is brought into contact with the other end face. Thus, a contact area when the ultrasonic waves are supplied is reduced compared to a case where flat end faces are directly brought into contact with each other without providing the projected portion. The energy of the supplied ultrasonic waves are concentrated on a contact portion between the projected portion and the corresponding end face. This provides a larger ultrasonic melting effect, with the result that a greater adhesion strength against a bending force is obtainable.
It is further preferable to differ a bending adhesion strength (i.e., a minimum bending load which causes the separation of the adhered faces when the bending load acts on the liquid applicator) between the bottom end face of the lead stepped portion and the lead end face of the bottom stepped portion at the respective adhered portions.
In this arrangement, the bending adhesion strength between the bottom end face of the lead stepped portion and the lead end face of the bottom stepped portion differs at the respective adhered portions, which increases the probability of separating the adhered faces at the adhered portion having a low bending adhesion strength. This in return prevents the separation of the adhered faces at the adhered portion having a high bending adhesion strength. In other words, the simultaneous separation of the adhered faces at both the adhered portions is prevented actively, thereby protecting the adhered portion having the high bending adhesion strength. As a result, the coupling of the lead and bottom side shafts and the airtightness in the liquid applicator can be maintained satisfactorily with the protected adhered portion.
As a means for differing the bending adhesion strength at the respective adhered portions, the following three arrangements can be considered. According to the first arrangement, two pairs of the lead and bottom stepped portions to be adhered with each other are formed such that the pair whose shortest distance between the adhered faces thereof and a lead end face of the lead side shaft or bottom end face of the bottom side shaft (i.e. a distance to an ultrasonic horn to be placed at an end of the liquid applicator) is shorter than that of the other pair has a larger radial thickness than the other pair. With this arrangement, the pair closer to the ultrasonic horn to be placed has a larger radial thickness. In other words, the pair at which a greater bending adhesion strength is obtainable due to an improved ultrasonic melting effect has a larger radial thickness. Accordingly, a difference in the bending adhesion strength between the pair closer to the ultrasonic horn and the other pair is widened further. Thus, when a large bending load acts on the liquid applicator, the adhered faces are liable to come apart only at the other pair distant from the ultrasonic horn.
According to the second arrangement, a loosely fitting portion to which the projected portion is fitted is formed on the face opposed to the projected portion at the pair of stepped portions having a shorter shortest distance i.e., closer to the ultrasonic horn to be placed, and the ultrasonic waves are supplied in a state where the projected portion is loosely fitted in the loosely fitting portion. With this arrangement, the loosely fitting portion is formed at the end face opposed to the projected portion at the pair of stepped portions which is allowed to obtain a greater bending adhesion strength due to an improved ultrasonic melting effect, and the ultrasonic waves are supplied while the projected portion is loosely fitted in the loosely fitting portion. Accordingly, the bending adhesion strength of the pair closer to the ultrasonic horn becomes further greater than that of the other pair. Thus, when a large bending load acts on the liquid applicator, the adhered faces are liable to come apart only at the other pair distant from the ultrasonic horn.
According to the third arrangement, the two pairs of lead and bottom stepped portions to be adhered are positioned relative to each other such that the opposing end faces of the pair more distant from the ultrasonic horn to be placed than the other pair are spaced apart by a specified distance when the faces of the other pair are in contact with each other. With this arrangement, the opposing end faces are spaced apart at the pair distant from the ultrasonic horn when those are in contact with each other at the pair closer to the ultrasonic horn placed at the end of the liquid applicator. By supplying the ultrasonic waves in this state, an amount of material melted by the ultrasonic wave is greater at the pair closer to the ultrasonic horn than at the pair distant therefrom. Accordingly, a difference in the bending adhesion strength between the pair closer to the ultrasonic horn to be placed and the other pair is widened further. Thus, when a large bending load acts on the liquid applicator the adhered faces are liable to come apart only at the other pair distant from the ultrasonic horn.
Further, either one of the lead side shaft or bottom side shaft may advantageously include outer, intermediate, and inner stepped portions arranged radially from an outermost side while the other shaft may include an auxiliary stepped portion opposed to at least one of the outer and inner stepped portions, and a fit-in stepped portion opposed to the intermediate stepped portion. The intermediate stepped portion is indented from the outer and inner stepped portions to thereby form a recessed portion between the outer and inner stepped portions. The fit-in stepped portion is formed so as to project from the auxiliary stepped portion. At least two pairs of stepped portions are adhered by means of ultrasonic adhesion in a state where the fit-in stepped portion is fitted in the recessed portion.
The above liquid applicator is fabricated by carrying out the ultrasonic adhesion in a state where the fit-in stepped portion is fitted in the recessed portion between the outer and inner stepped portions. This fit-in structure prevents the lead and bottom side shafts from being bent and deformed, thereby reducing the burden on the adhered portions in terms of the strength and preventing the separation of the adhered faces more reliably.
These and other objects, features and advantages of the present invention will become more apparent upon a reading of the following detailed description and accompanying drawings.